Multiple TagHelpers targeting same element cannot effectively communicate to children.

[NTaylorMullen]

With how TagHelpers work today if you have 2 TagHelpers targeting say a <form> tag and both do:

context.Items["MyContext"] = new MyContext { ... };

await context.GetChildContentAsync();

// Look to see what's changed

You run into some major issues if both TagHelpers try to do the same thing, only the first one actually detects changes in MyContext. This is due to how GetChildContentAsync works; it caches the result of the execution. One fix for this would be to always force un-cached execution of the child content but that's not really what the user wants to do.

[NTaylorMullen]

/cc @Eilon @DamianEdwards